In the transmission and distribution of pressurized gases and liquids, valves control a variable, such as pressure or flow rate, and operate at high pressure drops, that is, high pressure differentials between the upstream and downstream pressure. As such, in many instances these valves are fitted with actuators and positioners that respond to a control signal generated by a controller or computer. These valves are often referred to as “control valves.”
When a high pressure gas or liquid (“fluid”) is throttled through a control valve at a high pressure drop, aerodynamic noise is generated in the fluid and subsequently is propagated through the fluid, exiting the pipe walls (principally downstream), thereby causing noise to be propagated to the surrounding atmosphere. The result may be noise that exceeds allowable limits for worker hearing conservation.
A second concern involved with the throttling of a high pressure fluid through a control valve is that it often causes excessive mechanical vibration which results in attendant problems with the proper operation of associated measuring and controlling equipment. In addition, the vibration can also cause fatigue failure of welds or piping.
In order to reduce noise and mechanical vibration, inserts have been placed in the control valves. These inserts include a plurality of relatively small-diameter passages through which the fluid passes under certain flow conditions. Published U.S. Patent Application No. 2003-0178592 and U.S. Pat. No. 5,890,505 illustrate a noise reduction insert.
Control valves often are required for applications in which there is a high pressure drop throughout the entire range of travel of the valve. In these cases, the valves are designed for the continuous reduction of noise and mechanical vibration over their entire range of travel. U.S. Pat. No. 5,680,889 illustrates a valve of this type.
A prior art pressure reduction valve is manufactured by the assignee of the present application, Dresser, Inc., and sold under the trademark V-LOG. The V-LOG™ valve includes a trim having a plurality of flow resistance modules. U.S. Pat. No. 5,819,803, the disclosure of which is incorporated by reference, discloses a pressure reduction device that incorporates a plurality of flow resistance modules.
There are applications that involve a relatively high pressure drop at relatively low flow rates and small valve openings, and a relatively low pressure drop at maximum flow and relatively large valve openings. In the latter, low pressure-drop situation, a flow capacity is required that is higher than would be possible utilizing a valve designed for continuous noise reduction based on a high pressure drop throughout the entire valve travel range.
The valve of the present invention overcomes many limitations of prior art valves using the principle of “Herschel-Quincke tubes”. The invention uses the Herschel-Quincke tube concept alone and/or combined with other passive noise reduction elements, and as single elements or arranged in arrays to reduce the noise generated by a control valve. The Herschel-Quincke (abbreviated “H-Q”) tube is essentially a secondary flow path that branches off a main flow path and continues downstream for a certain length, L, recombining with the original main flow path (see FIGS. 1 and 2). The device reduces noise by diverting part of the acoustic wave traveling in the main flow path wave into the H-Q tube, the acoustic wave exits the tube out of phase with the main flow path acoustic wave, thus attenuating the main flow path noise.
Heretofore, Herschel-Quincke tubes have not been used in valve trim or as modular inserts in the fluid flow stream to attenuate noise generated by the valve. Burdisso et al. describes an invention using Herschel-Quincke tubes designed to reduce noise of the inlet and outlet ports of turbo-fan engines. (Burdisso, Ricardo and Ng, Wing, 2003, NASA/CR 2003-212097, Fan noise control using Herschel-Quincke Resonators). Ingard et al. describes a modified Herschel-Quincke tube designed to reduce duct noise. Ingard's device is fundamentally different from the present invention in that the device does not use a separate tube arrangement, but rather a flow splitter coupled with an expansion chamber to achieve the longer flow path described by Herschel and Quincke. (Brady, Lori, 2002 Masters Thesis Virginia Tech, Application of Herschel-Quincke tube Concept to Higher Order Acoustic Modes in Two-Dimensional Ducts).